Investigating Wave Ripples: Ripple Tank

A ripple tank is a shallow tray of water used to make and study water waves. It helps us see how waves behave: how they reflect, refract, and diffract, and how to measure wavelength, frequency, and speed.

Apparatus and setup

• Ripple tank, water, and a dipper (vibrator) to make ripples
• Lamp above and white paper or screen below to see bright and dark wavefront lines
• Plastic sheet or sloping plate to make a shallow region
• Barriers with a gap, and a straight barrier (mirror) for reflection

What you can show

Wave features

• Wavefronts: lines joining the crests (seen as bright lines). They show the direction the wave travels.
• Wavelength (λ): distance between two crests.
• Amplitude: height of the ripple (how tall the waves are).
• Frequency (f): number of waves passing a point each second.
• Wave speed (v): how fast a wavefront moves; linked by $v = f\,\lambda$.

Reflection at a plane surface

Aim a straight set of wavefronts at a straight barrier. The waves bounce off. The angle of incidence equals the angle of reflection. Wavefront spacing and speed stay the same.

Refraction due to change in depth

Send waves from deep to shallow water. In shallow water, waves move slower and the wavelength becomes shorter, but the frequency stays the same (the source controls f). Wavefronts bend towards the normal when entering the slower (shallow) region.

Diffraction through a gap or past an edge

Pass waves through a gap. If the gap is narrow (about the same size as $\lambda$), waves spread out widely in semicircles. A wide gap causes little spreading. Past a single edge, waves bend into the shadow region.

Measuring waves in the ripple tank

• Wavelength: freeze the pattern (use a strobe or a very low frequency) and measure the distance across several crests, then divide by the number of wavelengths.
• Frequency: count the number of crests passing a fixed point in 10 s and divide by 10.
• Speed: use $$v = f\,\lambda$$

Common misconceptions

• “Water travels across the tank.” In fact, the energy moves across; water mostly moves up and down.
• “Frequency changes in shallow water.” Frequency stays the same; speed and wavelength change.
• “Bigger gap means more diffraction.” Diffraction is greatest when gap size is similar to $\lambda$.

Real-world links

• Harbour entrances act like gaps: narrow entrances cause strong spreading of water waves.
• Sound around doorways diffracts into rooms; light diffracts much less because it has a tiny wavelength.